1. Field
The presently disclosed embodiment relates to a device for retaining a tank in an aircraft and more particularly one suited to holding cryogenic propellant tanks in a fuselage of an aircraft such as an airplane and notably a spaceplane. Such a device, which in the relevant art is referred to as a “supporting device”, is notably suited to supporting tanks of cylindrical or conical shape supplying a rocket motor of a spaceplane with propellant.
It affords a solution to applications that require cryogenic liquids to be transported in aircraft under very stringent space and mass constraints and for which usage and test cycles require that the tanks be set down and refitted at short order.
It particularly finds an application in spacecrafts which carry large quantities of cryogenic propellants used for the rocket propulsion of these craft and for which optimizing the dry weight is a prime concern.
2. Brief Description of Related Developments
In the field of space the non-structural cryogenic tanks of rocket stages are conventionally interfaced with the bearing structure of the stage that accommodates them via two skirt-like mounting devices situated above and below the tank.
These devices are designed to allow the tank fixing points to move radially as a result of thermal deformations of the cryogenic tank. The upper interface in this context allows longitudinal movements of the tank fixing points whereas the rear or lower interface on the other hand is longitudinally fixed.
These interface devices may be cones or link rod assemblies, as in the case of the inter-tank interface of the Ariane 5 cryogenic upper stage ESCA, as depicted in FIG. 1 which is a perspective half-view in which a tank A is restrained by link rods B on a structure C or may also be assemblies of connecting sheets.
These solutions entailing numerous connecting elements allow good distribution of load at the interfaces, but have the major disadvantages of a not-insignificant impact on the mass of the craft and the need for lengthy operation times for assembling and dismantling the interfaces.
Furthermore, the conventional launcher fixings are designed for forces essentially oriented along the axis of the tank, whereas for a spaceplane, the forces are not along this axis alone but also perpendicular to this axis and in terms of role. As a result, launcher solutions cannot be applied unmodified to an aircraft of the spaceplane type.
These interface devices are not, however, particularly well suited to compensating for the stresses induced by differential thermal expansions which are non-zero. Furthermore, they cause thermal losses that are not insignificant.
Finally, these devices are applicable very little if at all to installations in which the volume available for the supporting device is very small.
In the field of maritime transport, document U.S. Pat. No. 3,659,817 A describes a solution for supporting a cryogenic tank which consists of a set of fixings, at least 2×4 fixing elements, oriented tangentially to the skin of the cryogenic tank and perpendicular to the main axis thereof so as to avoid the generation of bending stresses in this same skin under the effect of the variations in orientation of the loads caused by the continuous motion of a ship at sea.
That document does not describe means suited to reacting the longitudinal loads along the tank main axis. Furthermore, the recurrent movements considered are of smaller amplitude by comparison with what a spaceplane for example might encounter between the aeronautical phase and the space phase, particularly when aeronautical certification requirements are taken into consideration. Finally, some of the support devices proposed for equalizing the stresses may prove highly penalizing in terms of mass when applied to rocket propulsion tanks. This is because this solution, like most of the solutions usually adopted for the maritime support of cryogenic tanks, essentially for liquid natural gas, is unable to optimize the entire tank+bearing structure+support elements mass package to the level required for the space or aeronautical domain. This is notably explained by the fact that the tanks used in maritime transport have a capacity of several hundreds of m3 and therefore dimensions of an order of magnitude greater than the tanks of a capacity of just a few m3 to which the presently disclosed embodiment relates. Likewise, thermal losses, which are negligible in comparison with the volumes transported in maritime transport, are no longer negligible on the scale of aeronautical craft and spacecraft.
In the field of the mounting of tanks in an airplane, documents U.S. Pat. No. 3,951,362 A and U.S. Pat. No. 3,979,005 A which apply to a toroidal tank describe support means which comprise supports for reacting shear forces distributed on the circumference of a cryogenic tank.
These supports consist of sheets of a curved shape to give them the flexibility needed to allow radial relative deformations and guarantee that they work purely in shear.
These supports, suited to tanks with toroidal bottoms, constitute just part of the support device which is more complex and requires either the addition in the airplane of a support structure of conical type, which is bulky and penalizing in terms of mass, or that the forces at the front of the tank be reacted on a pressurized end wall that is designed and engineered to perform this function and is therefore once again heavy and bulky.